From: "George Spelvin" <linux@horizon.com>
To: David.Laight@ACULAB.COM, linux-kernel@vger.kernel.org,
netdev@vger.kernel.org, tom@herbertland.com
Cc: mingo@kernel.org
Subject: Re: [PATCH v3 net-next] net: Implement fast csum_partial for x86_64
Date: 8 Feb 2016 15:12:34 -0500 [thread overview]
Message-ID: <20160208201234.8569.qmail@ns.horizon.com> (raw)
David Laight wrote:
> I'd need convincing that unrolling the loop like that gives any significant gain.
> You have a dependency chain on the carry flag so have delays between the 'adcq'
> instructions (these may be more significant than the memory reads from l1 cache).
If the carry chain is a bottleneck, on Broadwell+ (feature flag
X86_FEATURE_ADX), there are the ADCX and ADOX instructions, which use
separate flag bits for their carry chains and so can be interleaved.
I don't have such a machine to test on, but if someone who does
would like to do a little benchmarking, that would be an interesting
data point.
Unfortunately, that means yet another version of the main loop,
but if there's a significant benefit...
next reply other threads:[~2016-02-08 20:19 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-08 20:12 George Spelvin [this message]
2016-02-09 10:48 ` [PATCH v3 net-next] net: Implement fast csum_partial for x86_64 David Laight
2016-02-10 0:53 ` George Spelvin
2016-02-10 11:39 ` David Laight
2016-02-10 14:43 ` George Spelvin
2016-02-10 15:18 ` David Laight
[not found] <1454527121-4007853-1-git-send-email-tom@herbertland.com>
2016-02-04 9:30 ` Ingo Molnar
2016-02-04 10:56 ` Ingo Molnar
2016-02-04 19:24 ` Tom Herbert
2016-02-05 9:24 ` Ingo Molnar
2016-02-04 21:46 ` Linus Torvalds
2016-02-04 22:09 ` Linus Torvalds
2016-02-05 1:27 ` Linus Torvalds
2016-02-05 1:39 ` Linus Torvalds
2016-02-04 22:43 ` Tom Herbert
2016-02-04 22:57 ` Linus Torvalds
2016-02-05 8:01 ` Ingo Molnar
2016-02-05 10:07 ` David Laight
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